Gas turbine engines are often used to drive hydraulic or other loads, typically through a controllable clutch. At times, the gas turbine engine may experience an overload condition in excess of its performance limits. When such a condition arises, the gas turbine engine is unable to accelerate the driven load to the desired speed. In addition, if proper safety limits are not in place, this overload condition can also result in severe damage to the clutch.
Engine speed and acceleration in gas turbine engines are often controlled by controlling the rate of fuel flow supplied to the engine. For example, U.S. Pat. No. 4,432,201 to Hawes describes an acceleration/deceleration limiter circuit that maintains an acceleration limit for a closed loop fuel control of a gas turbine engine. If engine acceleration exceeds the acceleration limit, the closed loop control regulates the fuel flow to cause engine deceleration. To control engine acceleration during transient conditions in such a manner as to prevent engine stall, the system is also equipped with an acceleration limit reset circuit that changes the acceleration limit to accommodate the transient operating conditions. Similarly, U.S. Pat. No. 4,532,763 to Pisano describes an engine acceleration control system that effects precise control of fuel flow to control engine acceleration. A closed loop control system with feedback monitors various engine operating parameters to determine the operating acceleration of the engine and to determine therefrom the proper rate of fuel flow. The system is capable of performing acceleration control during normal operating conditions as well as transient operating conditions.
Further, U.S. Pat. No. 4,337,615 to LaCroix describes a gas turbine fuel control system that controls engine acceleration by varying the fuel flow to the engine to maintain an engine at an engine reference speed set point.
Although these prior art systems effectively control gas turbine engine acceleration, they do not control the driven load acceleration.